This invention relates generally to electronic devices having programmable memories and particularly to electronic devices such as radios that have programming ports for programming the memories.
Technological advances in the electronic area, particularly in the area of digital devices including microprocessors and solid state memory devices such as Programmable Read Only Memories (PROM'S) and Electrical Erasable Programmable Read Only Memories (EEPROM'S), have lead to significant changes in the design of electronic devices such as two-way radios.
Early generation radios utilized crystals for channel elements with individual crystals for each desired frequency. Such crystals were slaved to a channel selector switch along with additional features such as subaudible tone encoders and decoders. Other personality features of the radio were either hard wired discrete type circuitry or modules that were installed in order to provide the desired personality feature of a particular radio.
The development of frequency synthesizers provided a major advance in radio design by eliminating the requirement of individual channel elements for each desired frequency of operation. By utilizing a memory to maintain the necessary divisor information for use with the frequency synthesizer, any desired frequency within the operating range of the radio can be achieved simply by changing the divisor information in the memory. Such memory devices can also be used to store designators of appropriate subaudible tone information for the individual channel as well as other information.
The use of microprocessors in radios has greatly enhanced the flexibility of the radio design. While many desired functions such as scanning, can be achieved without the use of microprocessors, the microprocessor simplifies the radio design by allowing the manufacturer to build a single design and program the individual radios to have any or all of the possible available functions.
PROM's have been widely used as code plugs for containing channel information. The use of PROM's allows radios to be easily customized, that is, the particular desired channels of operation can be programmed into a PROM which is then inserted into a radio. A significant drawback to the use of PROM's is that, if it is desired to redefine the frequency information for the channels of operation, it is necessary to replace the PROM with a different PROM containing the desired information. Advances in the EEPROM art have removed this limitation.
Since EEPROM's are electrically erasable, they can be erased and reprogrammed while in place in the radio. This development has permitted radios to be built with a great degree of flexibility, in that the characteristics of each individual radio can be reprogrammed with relative ease.
In order to provide for programming of such radios, a connector or port is provided on the radio for programming purposes. Such a port, by allowing ready access for programming, is useful to both the manufacturer and the user of the radio. The ease of programming does however present a problem, in that it is difficult to prevent unauthorized reprogramming of the device. For example, metropolitan police departments are sensitive to the theft of their radios. It is a particular concern to them that a stolen radio can be easily reprogrammed to operate on any other of their frequencies. Consequently, it is desirable to provide means for preventing the unauthorized reprogramming of such radios.